Method and apparatus for processing navigation data in position determination

ABSTRACT

Methods and apparatuses for the processing of false alarms in position determination. At least one embodiment of the present invention estimates and uses measurement false alarm probabilities in the position determination process. In one embodiment, the estimated measurement false alarm probabilities are combined to determine the reliability of the determined position solution or the reliability of the set of measurements as a collection. In one embodiment, the estimated measurement false alarm probabilities are used in the isolation and elimination of faulty measurements. For example, the traditional geometry based metric for identifying a faulty measurement is further weighted according to the measurement false alarm probabilities in order to determine the faulty measurement.

RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional ApplicationNo. 60/447,506, filed Feb. 14, 2003, and U.S. Provisional ApplicationNo. 60/493,536, filed on Aug. 7, 2003.

FIELD OF THE INVENTION

[0002] The invention relates to position determination systems, and moreparticularly to the processing of false alarms.

BACKGROUND

[0003] To perform position location in wireless cellular networks (e.g.,a cellular telephone network), several approaches perform triangulationbased upon the use of timing information sent between each of severalbase stations and a mobile device, such as a cellular telephone. Oneapproach, called Advanced Forward Link Trilateration (AFLT) or EnhancedObserved Time Difference (EOTD), measures at the mobile device the timesof arrival of signals transmitted from each of several base stations.These times are transmitted to a Position Determination Entity (PDE)(e.g., a location server), which computes the position of the mobiledevice using these times of reception. The transmit times at these basestations are coordinated such that at a particular instance of time, thetimes-of-day associated with multiple base stations are within aspecified error bound. The accurate positions of the base stations andthe times of reception are used to determining the position of themobile device.

[0004]FIG. 1 shows an example of an AFLT system where the times ofreception (TR1, TR2, and TR3) of signals from cellular base stations101, 103, and 105 are measured at the mobile cellular telephone 111.This timing data may then be used to compute the position of the mobiledevice. Such computation may be done at the mobile device itself, or ata location server if the timing information so obtained by the mobiledevice is transmitted to the location server via a communication link.Typically, the times of receptions are communicated to a location server115 through one of the cellular base stations (e.g., base station 101,or 103, or 105). The location server 115 is coupled to receive data fromthe base stations through the mobile switching center 113. The locationserver may include a base station almanac (BSA) server, which providesthe location of the base stations and/or the coverage area of basestations. Alternatively, the location server and the BSA server may beseparate from each other; and, the location server communicates with thebase station to obtain the base station almanac for positiondetermination. The mobile switching center 113 provides signals (e.g.,voice communications) to and from the land-line Public SwitchedTelephone System (PSTS) so that signals may be conveyed to and from themobile telephone to other telephones (e.g., land-line phones on the PSTSor other mobile telephones). In some cases the location server may alsocommunicate with the mobile switching center via a cellular link. Thelocation server may also monitor emissions from several of the basestations in an effort to determine the relative timing of theseemissions.

[0005] In another approach, called Time Difference of Arrival (TDOA),the times of reception of a signal from a mobile device is measured atseveral base stations (e.g., measurements taken at base stations 101,103 and 105). FIG. 1 applies to this case if the arrows of TR1, TR2, andTR3 are reversed. This timing data may then be communicated to thelocation server to compute the position of the mobile device.

[0006] Yet a third method of doing position location involves the use inthe mobile device of a receiver for the United States Global PositioningSatellite (GPS) system or other Satellite Positioning System (SPS), suchas the Russian GLONASS system and the proposed European Galileo System,or a combination of satellites and pseudolites. Pseudolites areground-based transmitters, which broadcast a PN code (similar to a GPSsignal) modulated on an L-band carrier signal, generally synchronizedwith SPS time. Each transmitter may be assigned a unique PN code so asto permit identification by a remote receiver. Pseudolites are useful insituations where SPS signals from an orbiting satellite might beunavailable, such as tunnels, mines, buildings or other enclosed areas.The term “satellite”, as used herein, is intended to include pseudolitesor equivalents of pseudolites, and the term GPS signals, as used herein,is intended to include GPS-like signals from pseudolites or equivalentsof pseudolites. Such a method using a receiver for SPS signals may becompletely autonomous or may utilize the cellular network to provideassistance data or to share in the position calculation. As shorthand,we call these various methods “SPS”. Examples of such methods aredescribed in U.S. Pat. Nos. 6,208,290; 5,841,396; 5,874,914; 5,945,944;and 5,812,087. For instance, U.S. Pat. No. 5,945,944 describes a methodto obtain from cellular phone transmission signals accurate timeinformation, which is used in combination with SPS signals to determinethe position of the receiver; U.S. Pat. No. 5,874,914 describes a methodto transmit the Doppler frequency shifts of in view satellites to thereceiver through a communication link to determine the position of thereceiver; U.S. Pat. No. 5,874,914 describes a method to transmitsatellite almanac data (or ephemeris data) to a receiver through acommunication link to help the receiver to determine its position; U.S.Pat. No. 5,874,914 also describes a method to lock to a precisioncarrier frequency signal of a cellular telephone system to provide areference signal at the receiver for SPS signal acquisition; U.S. Pat.No. 6,208,290 describes a method to use an approximate location of areceiver to determine an approximate Doppler for reducing SPS signalprocessing time; and, U.S. Pat. No. 5,812,087 describes a method tocompare different records of a satellite data message received atdifferent entities to determine a time at which one of the records isreceived at a receiver in order to determine the position of thereceiver. In practical low-cost implementations, both the mobilecellular communications receiver and the SPS receiver are integratedinto the same enclosure and, may in fact share common electroniccircuitry.

[0007] In yet another variation of the above methods, the round tripdelay (RTD) is found for signals that are sent from the base station tothe mobile device and then are returned. In a similar, but alternative,method the round trip delay is found for signals that are sent from themobile device to the base station and then returned. Each of theseround-trip delays is divided by two to determine an estimate of theone-way time delay. Knowledge of the location of the base station, plusa one-way delay constrains the location of the mobile device to a circleon the earth. Two such measurements from distinct base stations thenresult in the intersection of two circles, which in turn constrains thelocation to two points on the earth. A third measurement (even an angleof arrival or cell sector) resolves the ambiguity.

[0008] A combination of either the AFLT or TDOA with an SPS system iscalled a “hybrid” system. For example, U.S. Pat. No. 5,999,124 describesa hybrid system, in which the position of a cell based transceiver isdetermined from a combination of at least: i) a time measurement thatrepresents a time of travel of a message in the cell based communicationsignals between the cell based transceiver and a communication system;and, ii) a time measurement that represents a time of travel of an SPSsignal.

[0009] Altitude aiding has been used in various methods for determiningthe position of a mobile device. Altitude aiding is typically based on apseudo-measurement of the altitude. The knowledge of the altitude of alocation of a mobile device constrains the possible positions of themobile device to a surface of a sphere (or an ellipsoid) with its centerlocated at the center of the earth. This knowledge may be used to reducethe number of independent measurements required to determine theposition of the mobile device. For example, U.S. Pat. No. 6,061,018describes a method where an estimated altitude is determined from theinformation of a cell object, which may be a cell site that has a cellsite transmitter in communication with the mobile device.

[0010] When a minimum set of measurements are available, a uniquesolution to the navigation equations can be determined for the positionof the mobile station. When more than one extra measurement isavailable, the “best” solution may be obtained to best fit all theavailable measurements (e.g., through a least square solution procedurethat minimizes the residual vector of the navigation equations). Sincethe residual vector is typically non-zero when there are redundantmeasurements, due to the noises or errors in the measurements, anintegrity-monitoring algorithm can be used to determine if all themeasurements are consistent with each other. For example, a traditionalReceiver Autonomous Integrity Monitoring (RAIM) algorithm may be used todetect if there is a consistency problem in the set of the redundantmeasurements. For example, one RAIM algorithm determines if themagnitude of the residual vector for the navigation equations is below athreshold value. If the magnitude of the residual vector is smaller thanthe threshold, the measurements are considered consistent. If themagnitude of the residual vector is larger than the threshold, there isan integrity problem, in which case one of the redundant measurementsthat appears to cause the most inconsistency may then be removed toobtain an improved solution.

SUMMARY OF THE DESCRIPTION

[0011] Methods and apparatuses for the processing of false alarms inposition determination are described here. Some of the embodiments ofthe present invention are summarized in this section.

[0012] At least one embodiment of the present invention estimates anduses measurement false alarm probabilities in the position determinationprocess. In one embodiment, the estimated measurement false alarmprobabilities are combined to determine the reliability of thedetermined position solution or the reliability of the set ofmeasurements as a collection. In one embodiment, the estimatedmeasurement false alarm probabilities are used in the isolation andelimination of faulty measurements. For example, the traditionalgeometry based metric for identifying a faulty measurement is furtherweighted according to the measurement false alarm probabilities in orderto determine the faulty measurement.

[0013] In one aspect of the present invention, a method of positiondetermination for a mobile station includes: determining a firstmeasurement (e.g., a time of arrival of a GPS or base station signal, apseudorange) for position determination for the mobile station fromposition determination signals received at the mobile station; anddetermining a first reliability indicator from the signals for the firstmeasurement, where the first reliability indicator represents a level ofmeasurement false alarm probability for the first measurement. In oneexample, a reliability level is determined from the first reliabilityindicator to represent a probability that a position solution calculated(e.g., at the mobile station, a remote server) for the mobile stationusing the measurement is not false. In one example, the firstmeasurement and the first reliability indicator are transmitted to aremote server for position determination of the mobile station. In oneexample, one or more signal quality indicators, which are determinedfrom the signals for the first measurement, are transmitted from themobile station to a remote server; and, the first reliability indicatoris determined at the remote server using the one or more signal qualityindicators. In one example, a second measurement is determined fromposition determination signals received at the mobile station; a secondreliability indicator is determined from position determination signalsfor the second measurement to represent a level of measurement falsealarm probability for the second measurement; a position solution iscalculated for the mobile station using the first and secondmeasurements; and the first and second reliability indicators arecombined to determine a reliability of the position solution. In oneexample, when the measurements are not consistent, one of the first andsecond measurements is eliminated from position determination using thefirst and second reliability indicators. In one example, the firstreliability indicator is determined from at least one of: a) magnitudeof a correlation peak; b) correlation peak width; c) signal strength; d)signal to noise ratio; e) signal to interference ratio; f) relationshipof a correlation peak used for determination of the first measurementwith one or more candidate peaks; and g) relationship of signals fordetermination of the first measurement with detected signals.

[0014] In one aspect of the present invention, a method of positiondetermination for a mobile station includes: combining a plurality ofmeasurement false alarm indicators to determine a reliability of aposition calculated using a plurality of measurements, where theplurality of measurement false alarm indicators represent levels of apriori false alarm probability for the plurality of measurementsrespectively. In one example, the position for the mobile station iscalculated using the plurality of measurements; each of the plurality ofmeasurement false alarm indicators is a value of more than two levels(e.g., a number within a range, such as between 0 and 1). In oneexample, one of the plurality of measurement false alarm indicators isdetermined from one or more signal quality indicators (e.g., a)magnitude of a correlation peak; b) correlation peak shape indicator; c)signal strength; d) signal to noise ratio; and e) signal to interferenceratio).

[0015] In one aspect of the present invention, a method of positiondetermination for a mobile station includes: eliminating one of aplurality of measurements from position determination using a pluralityof a priori false alarm indicators in response to a determination thatthe plurality of measurements are not consistent, where the plurality ofa priori false alarm indicators are determined respectively for theplurality of measurements individually. In one example, the eliminatedone of the plurality of measurements is determined from comparing theplurality of a priori false alarm indicators. In one example, aplurality of inconsistency indicators are determined for the pluralityof measurements respectively from the plurality of measurements; and,the eliminated one of the plurality of measurements is determined fromweighting the plurality of inconsistency indicators according to theplurality of a priori false alarm indicators respectively. In oneexample, whether or not an inconsistency level among the plurality ofmeasurements is above a threshold is determined; and the plurality of apriori false alarm indicators are determined from signals used fordetermination of the plurality of measurements respectively.

[0016] The present invention includes methods and apparatuses whichperform these methods, including data processing systems which performthese methods, and computer readable media which when executed on dataprocessing systems cause the systems to perform these methods.

[0017] Other features of the present invention will be apparent from theaccompanying drawings and from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention is illustrated by way of example and notlimitation in the figures of the accompanying drawings in which likereferences indicate similar elements.

[0019]FIG. 1 shows an example of a prior art cellular network whichdetermines the position of a mobile cellular device.

[0020]FIG. 2 shows an example of a server which may be used with thepresent invention.

[0021]FIG. 3 shows a block diagram representation of a mobile stationaccording to one embodiment of the present invention.

[0022]FIG. 4 shows examples of different probability distributions forfalse alarms and for normal measurements, which may be used in thepresent invention.

[0023]FIG. 5 illustrates a method to determine the probability of twomeasurements being close to each other, which may be used in the presentinvention.

[0024]FIG. 6 illustrates a method to determine the probability that twomeasurements are false alarms according to one embodiment of the presentinvention.

[0025]FIG. 7 shows a method to determine the position of a receiveraccording to one embodiment of the present invention.

[0026]FIG. 8 shows a detailed method to determine the position of amobile station according to one embodiment of the present invention.

[0027]FIG. 9 shows another detailed method to determine the position ofa mobile station according to one embodiment of the present invention.

DETAILED DESCRIPTION

[0028] The following description and drawings are illustrative of theinvention and are not to be construed as limiting the invention.Numerous specific details are described to provide a thoroughunderstanding of the present invention. However, in certain instances,well known or conventional details are not described in order to avoidobscuring the description of the present invention. References to one oran embodiment in the present disclosure are not necessary to the sameembodiment; and, such references means at least one.

[0029] At least one embodiment of the present invention seeks toestimate and use measurement false alarm probabilities in the positiondetermination process.

[0030] In the determination of the position of a mobile station or otherdevice, a position calculation typically uses a number of geometricallydistinct measurements, such as range, pseudorange, round trip delay andothers that are associated with distinct reference points (e.g., GPSsatellites, pseudolites, base stations, surface of the earth). Anobtained measurement may be in fact a false alarm, which is typicallycaused by a poor signal condition such that an irrelevant signal ismistakenly identified for the determination of the measurement.

[0031] There are many conditions that can cause false alarms. Forexample, in acquiring a GPS signal, a local reference signal with apseudorandom noise code is correlated with the received GPS signals. Thecorrelation output reaches a peak when the timing of the local referencesignal and the GPS signal of the same pseudorandom noise code matches. Apseudorange is then determined from the timing of the referencepseudorandom noise code. When the signal strength is low, a noise spike(e.g., due to the thermal noises) in the correlation output may beselected as a measurement, causing a false alarm. Typically, acorrelation peak that is above a threshold is selected for thedetermination of a pseudorange. The threshold is typically designed sothat the probability of false alarm when a peak is above the thresholdis below a specified level. To reduce the probability of false alarm, ahigh threshold may be used. However, since the correlation peaks belowthe threshold are ignored, the high threshold reduces the measurementavailability when the signal strength is low.

[0032] Signal interference can also cause false alarms. For example, thelocal reference signal may cross correlate with a strong GPS signal of adifferent pseudorandom noise code. The correlation output of the signalswith different pseudorandom noise code typically has small correlationpeaks. When the cross correlated GPS signal is strong while the GPSsignal to be acquired is relatively weak, these cross correlation peaksmay be above the threshold, causing false alarms. Similarly, when theGPS signal with the same pseudorandom noise code is very strong, thesmall correlation peaks occurred at a number of different timingdifferences in auto correlation may also be above the threshold, causingfalse alarms. The relationship of the GPS signals used for thedetermination of an obtained measurement with other detected GPS signalscan be used in the estimation of the probability of false alarms due tocross correlation.

[0033] Multi-path signals can also cause false alarms. The reflection ofa GPS signal through a different path causes additional delay. In somecases, the indirect GPS signal may be stronger than the direct GPSsignal. Thus, when the direct GPS signal is weak, the multi-path signalsmay be used for determination of the measurement. Since the multi-pathsignal arrives later than the direct signal, the relationship of thecorrelation peak used for the determination of an obtained measurementwith one or more candidate peaks can be used in the estimation of theprobability of false alarms. Further, multi-path signals may change theshape of a correlation peak (e.g., the width of a correlation). Thus, ameasurement of the shape of the correlation peak can also be used as asignal quality indicator in the determination of the probability offalse alarms.

[0034] Further, interference from some other signal sources (e.g.,jammer, or communication signals) may also cause false alarms. Thus, anumber of signal quality indicators (e.g., correlation peak magnitude,signal to noise ratio, signal to interference ratio, signal strength,relationship of a correlation peak with candidate peaks, relationship ofsignals for measurement with other detected signals, and others) can beused for the determination of the false alarm probabilities according toembodiments of the present inventions. In the design of a traditionalreceiver, some of the signal quality indicators have been used in thedetermination of threshold values (e.g., correlation output threshold)such that the obtained measurements that meet these thresholds have afalse alarm probability small than a target value. In one embodiment ofthe present invention, a number of different levels of threshold valuesare used to estimate the false alarm probabilities for individualmeasurements. These a priori false alarm probabilities are estimatedwithout combining different geometrically distinct measurements that areassociated with different reference points (e.g., different GPSsatellites or base stations). These a priori false alarm probabilitiesare based on the statistical data, not on the consistency betweendifferent and distinct geometric measurements. In one embodiment of thepresent invention, different levels of threshold values are used toestimate the discrete levels of false alarm probabilities. In oneembodiment, an interpolation scheme is used to determine the false alarmprobabilities based on the measured signal quality indicators (e.g.,using an empirical formula). The relation between the false alarmprobabilities and the signal quality indicators can be obtained fromvarious approaches known in the art, such as from collecting statisticaldata, numerical modeling, numerical simulation, analytical analysis, andothers.

[0035] In additional to the range information (e.g., the pseudorange),other types of measurements may also be false alarms. For example, theidentity of a base station may be an error from base station lookupoperations. Some base stations have the same identification strings.Thus, there is a chance that the base station is mistakenly identified.Currently, base station lookups use the probabilities of being correctin their determination. These probabilities can be further used inembodiments of the present invention.

[0036] In a traditional system, the measurements are individuallyrequired to meet a minimum threshold of reliability so that the chancesof the measurements as false alarms are smaller enough in order to usethe measurements in the position determination calculation. If themeasurement does not meet the reliability threshold, the measurement isdiscarded as a false alarm (or the measurement is not made at all, e.g.,when the correlation peaks are below the threshold). Thus, thetraditional system uses the measurement in the calculation of theposition only if the measurement meets a strict reliability threshold.

[0037] At least one embodiment of the present invention uses a morecomplete approach to estimate and use various degrees of measurementreliability in a navigation solution. The probabilities of individualmeasurements as false alarms (or the converse, the measurementreliabilities) are estimated and used in the position calculation stageto determine the probability that the position itself is false. In oneembodiment, the estimate of a false alarm probability is expressed as avalued between 0 or 1 for both measurement and the final positioncalculation. In one embodiment, the estimation of measurement falsealarm probability is performed at the source of the measurement (e.g.,an SPS receiver) and transmitted to a remote server along with theassociated measurements for position determination. The server mayfurther refine the false alarm probability estimates (e.g., usinginformation available at the server) before using the values in positiondetermination.

[0038] Typically, a false alarm measurement and a correspondingnon-false alarm measurement have very different probabilitydistributions. If a measurement of a parameter is not a false alarm, themeasurement typically has a probability distribution that isconcentrated in a small range near the true value of the parameter(e.g., according to a Gaussian distribution). However, if themeasurement is a false alarm, the measurement typically has aprobability distribution over a wide range around the true value of theparameter to be measured (e.g., a relative uniform distribution).

[0039]FIG. 4 shows examples of different probability distributions forfalse alarms and for normal measurements, which may be used in thepresent invention. In FIG. 4, curve 401 shows a distribution of ameasurement (e.g., pseudorange) if it is a false alarm. The false alarmmeasurement is distributed within a wide range D₁ (411). Curve 403 showsa distribution of the measurement when it is not a false alarm. Thedistribution of the measurement that is not a false alarm isconcentrated in a small range D₂ (413). One embodiment of the presentinvention determines a probability of false alarm in view of therelation between the obtained measurements using the distinctdistribution patterns of the false alarm measurement and non-false alarmmeasurement.

[0040] For example, when a threshold for a measurement false alarmprobability is 0.001, the false alarm probabilities of 0.01 for a firstmeasurement of and 0.02 for a second measurement are significantly worsethan the threshold. However, if the first measurement agrees well withthe second measurement, the first and second measurements can becombined as one measurement, which is a false alarm only when both ofthe first and second measurements are false alarm. Thus, if the firstand second measurements are independent from each other, the probabilityof false alarm for the combined measurement is 0.01×0.02=0.0002, whichis significantly better than the threshold of 0.001. Thus, thesecombined measurements of low reliability can be used, when they agreewith each other, without compromising the reliability of the solution.

[0041]FIG. 5 illustrates a method to determine the probability of twomeasurements being close to each other, which may be used in the presentinvention. For illustration purpose, it is assumed that both of the twomeasurements have the same uniform distribution in the range D (507).When the first measurement is at point x_(p) (505), the secondmeasurement must be in the range 509 if the second measurement is withina distance d to the first measurement. Thus, from the probabilitydistributions of the first and second measurements, one can obtain theprobability that two measurements are within a distance of d. AlthoughFIG. 5 illustrates a situation where the two measurements have the sameuniform distribution, from this description, a person skilled in the artwill understand that such a probability can be determined for twomeasurements of the same distribution or different distributions.

[0042]FIG. 6 illustrates a method to determine the probability that twomeasurements are false alarms according to one embodiment of the presentinvention. From the false alarm distribution and the non-false alarmdistribution (e.g., curves 401 and 403 in FIG. 4), one can determinerespectively the probabilities that both measurements are within adistance of d, as illustrated with FIG. 5. For example, curve 601 showsthe probability of two false alarm measurements being within a givendistance d; and curve 603 shows the probability of two non-false alarmmeasurements being within a given distance d. Thus, for a small distanced_(T), there is a huge difference between the probability of two falsealarm measurements being with d_(T) (at point 611) and the probabilityof two non-false alarm measurements being with d_(T). Thus, when twoobtained measurements are within a small distance, it is very likelythat the two measurements are non-false alarm measurements; when the twoobtained measurements are separated apart by a large distance, it isvery likely that at least one of the two measurements is a false alarm.

[0043] For example, if 1) both a first measurement and a secondmeasurement are determined within [−1,1] if they are not false alarmsbut within [−1000, 1000] if they are false alarms and 2) both the firstand second measurements have a probability of 0.2 as a false alarm, thechance that these two measurements are lined up so precisely, out ofsheer luck as false alarms, is very low. Thus, these two measurementsare more likely not false alarms. However, if both the first and secondmeasurements have the same probability of 0.2 as a false alarm within[−1000, 1000] but the first measurement is determined to be within[−1,1] and the second measurement within [9,11], the chance of both ofthe two measurements as non-false alarms is very small, since the twomeasurements are so far misaligned.

[0044] In one embodiment of the present invention, the probability ofthe two measurements are false alarm measurements when the twomeasurements are determined to be within a given distance d isdetermined (or estimated) from the probabilities of the individualmeasurements as false alarms, the probability of the measurements beingwithin a distance d if the measurements are false alarms, and theprobability of the measurements being within a distance d if themeasurements are non-false alarms. For example, let C_(d) represent thatthe two measurements are within a distance d; F represent that the twomeasurements are false alarms; and N represent that at least one of thetwo measurements is not a false alarm, one may use the followingexpression.

P(F|C _(d))/P(N|C _(d))=[P(C|F) P(F)]/[P(C|N)P(N)]

[0045] where P(C|F) is the probability of the two measurements beingwithin a distance d when the two measurements are false alarms; P(C|N)is the probability of the two measurements being within a distance dwhen the two measurements are non-false alarms; P(F) and P(N) are theprobabilities of the two measurements being false alarms and not allfalse alarms respectively; and, P(F|C_(d)), P(N|C_(d)) are theprobabilities of the two measurements being false alarms and being notall false alarms when the two measurements are within a distance d.P(F), P(N), P(F|C_(d)) and P(N|C_(d)) can be determined from theestimated a priori measurement false alarm probabilities and thedistributions of the false alarm measurements and the non-false alarmmeasurements respectively. From this description, it will be apparent toone skilled in the art that the false alarm probabilities for individualmeasurements, the relation between the individual measurements and theprobability distribution for the measurements as false alarms ornon-false alarms can be used to compute the posterior probability of thesolution being a false alarm.

[0046] In one embodiment of the present invention, the threshold formeasurement reliability is reduced so that less reliable measurementsare used in position determination. This can improve the sensitivitywithout compromising the final reliability of the position solution. Forexample, when a high measurement reliability threshold is used, theremay be only three measurements available, not enough for thedetermination of a portion. However, when the threshold is slightlylowered, addition two or more measurements may become available. Makinguse of the false alarm probabilities of the additional measurements andthe relation of the measurements (e.g., a measurement of the closenessof the measurement, such as a distance between a position solutionobtained using one of the low reliability measurements with the threehigh reliability measurements and another position solution obtainedusing another one of the low reliability measurements with the threehigh reliability measurements), one can determine whether or not therelation between the measurements improves the posterior probability ofthe measurements as false alarms to a level such that the reliability ofthe final solution is not compromised.

[0047] In one embodiment of the present invention, the a priorimeasurement false alarm probabilities, those determined before anintegrity check is performed, are used in identifying the measurement atfault. For example, when an integrity problem is detected (e.g., using atraditional RAIM/SMO method), a traditional method may be used toidentify a faulty measurement based on the redundant measurements. Whena lower threshold for measurement false alarm probabilities is used, thechance to have more redundant measurements increases. Further, in oneembodiment of the present invention, the a priori false alarmprobabilities of the measurements are also used in identifying thefaulty measurement. In one embodiment of the present invention, thetraditional measure for determining the faulty measurement (e.g., ageometry based metric) is combined with the a priori false alarmprobabilities to determine an indicator for identifying the faultymeasurement. For example, the traditional measure may be weighted by thea priori false alarm probabilities to determine the faulty measurement.When both the geometry based metric and the a priori false alarmprobability indicators are expressed in terms of probabilities, theseprobabilities can be combined (e.g., multiplied) to generate anindicator so that the measurement with the worst indicator is removed.Alternatively, a threshold may be used to identify the faultymeasurement if the traditional metric for one of the measurements isworse than the threshold; however, when the traditional method fails toidentify the faulty measurement (e.g., when all values are bellow thethreshold), the faulty one is then identified according to the a priorifalse alarm probabilities. From this description, one skilled in the artcan envision many combinations and variations of the methods to use thea priori measurement false alarm probabilities in identifying andeliminating faulty measurements.

[0048] In one embodiment of the present invention, even when nointegrity problem is detected (e.g., by a traditional RAIM method), theindividual measurement reliability values, the geometry, and internalconsistency are combined to determine the likelihood that the finalsolution fits its Gaussian error estimate, or is a false alarm positionreport. When the false alarm probability of a calculated position is lowenough, the calculated position can be reported to the end user.Alternatively, the calculated position can be reported to the end userwith the reliability indicator (e.g., regardless of the reliabilitylevel of the position solution).

[0049]FIG. 7 shows a method to determine the position of a receiveraccording to one embodiment of the present invention. Operation 701determines, at a receiver, a measurement (e.g., a pseudo-range, a roundtrip time, an identification of a base station) and a false alarmprobability indicator for the measurement from signals received at thereceiver. In one embodiment of the present invention, each individuallymeasurement has an associated false alarm probability determined basedon received signals (e.g., magnitude of the correlation peak,correlation peak shape/width, signal strength, signal to noise ratio,signal to interference ratio, a relationship of a correlation peak usedfor the determination of the measurement with other candidate peaks,such as peak ratio, peak interval, and relationship of the GPS signalfor the determination of the measurement with other detected GPSsignals). In one embodiment of the present invention, a false alarmprobability indicator shows the reliability of the measurement in one ofa predetermined number of levels. In one embodiment, the false alarmprobability indicator is a number in the range [0,1]. In one embodimentof the present invention, the receiver determines the false alarmprobability indicator based on the signal quality indicators (e.g.,magnitude of the correlation peak, correlation peak width, signalstrength, signal to noise ratio, signal to interference ratio,relationship with other candidate peaks, and relationship with other GPSsignals detected) using a pre-determined formula (e.g., an empiricalformula based on statistical data, or one based on numerical/analyticalprobability analysis). Alternatively, the receiver can transmit one ormore signal quality indicators to a remote server, which determinesand/or improves the false alarm probability for the measurement based onthe signal quality indicators. Operation 703 determines a position ofthe receiver using the measurement and the false alarm probabilityindicator. In one embodiment of the present invention, the false alarmprobability indicator is used to determine the reliability of theposition solution that is based on the measurement (or the reliabilityof the redundant measurements as a set). In another embodiment of thepresent invention, the false alarm probability indicator is used toselect a faulty measurement when an integrity problem is detected (e.g.,when there is inconsistency among the measurements used in determiningthe position). Further, in one embodiment of the present invention, therange over which a false alarm may occur is also determined. Differentsources for false alarms may have different distributions over differentranges, which may be determined or improved at a remote server. In oneembodiment of the present invention, the risk of a particular type offalse alarm condition is identified to better identify the false alarmdistribution, which is used in testing the consistency of measurements,determining whether an alignment of low reliability measurements isconsistent.

[0050]FIG. 8 shows a detailed method to determine the position of amobile station according to one embodiment of the present invention.Operation 801 determines, at a mobile station, a first measurement(e.g., a pseudo-range, a round trip time, an identification of a basestation) and a first false alarm probability indicator for the firstmeasurement from signals received at the mobile station. Operation 803determines, at the mobile station, a second measurement (e.g., apseudo-range, a round trip time, an identification of a base station)and a second false alarm probability indicator for the secondmeasurement from signals received at the mobile station. Operation 805transmits the first and second measurements and the first and secondfalse alarm probability indicators from the mobile station to a remoteserver. Operation 807 determines, at the remote server, a position ofthe mobile station using the first and second measurements. Operation809 determines, at the remote server, whether or not the position isacceptable using the first and second false alarm probabilityindicators. For example, the first and second false alarm probabilityindicators are combined to determine the reliability of the positionsolution. If operation 811 determines that the measurements are notconsistent, when redundant measurements are available for autonomousintegrity monitoring, operation eliminates a faulty measurement usingthe first and second false alarm probability indicators. For example,the first and second false alarm probability indicators are used indetermining which one of the first and second measurements is faulty.For example, the inconsistency indicators of traditional methods for thefirst and second measurements are weighted respectively according to thefirst and second false alarm probability indicators in identifying andeliminating the faulty measurement.

[0051]FIG. 9 shows another detailed method to determine the position ofa mobile station according to one embodiment of the present invention.Operation 901 determines, at a mobile station, a plurality ofmeasurements (e.g., a pseudo-range, a round trip time, an identificationof a base station) from signals received at the mobile station.Operation 903 determines, at the mobile station, a first false alarmprobability indicator for a first one of the plurality of themeasurements from signals received at the mobile station. Operation 905transmits the plurality of measurements and the first false alarmprobability indicator from the mobile station to a remote server.Operation 907 determines, at the remote server, a second false alarmprobability indicator for the first one of the plurality of measurementsfrom the first false alarm probability indicator using informationavailable at the remote server. For example, the server may maintain astatistical data about the false alarms as a function of the indicatorsprovided by the receiver, which can be used to refine the probability ofthe measurement false alarms. Further, the server may accumulate andimproved the statistical data based the information collected during theposition determination service. Operation 909 determines, at the remoteserver, a position of the mobile station from the first and secondmeasurements. Operation 911 determines, at the remote server, aprobability of whether or not the position is false using the secondfalse alarm probability indicator. Further, when redundant measurementsare not inconsistent, the second false alarm probability indicator canbe used in eliminating the faulty measurement.

[0052] Thus, the methods of the present invention allow improvedreliability. The measurement that is most likely to be a false alarm canbe more reliably selected. A specific metric can be provided with thesolution to indicate the reliability of the solution based on a priorifalse alarm probability indicators. Further, the methods of the presentinvention allow improved sensitivity and availability. Lower thresholdsmay be used for the individual measurements so that the chance of havingthe minimum number of measurements or more for the positiondetermination is increased. Since the combination of lower reliabilitymeasurements may be determined to have a high reliability finalsolution, this allows greater availability of GPS and AFLT measurementsand more frequent accurate solutions. Embodiments of the presentinvention include the process of estimating the false alarm probabilityof a given measurement at the mobile by examining the characteristics ofthe selected signals. These characteristics may include signal strength,correlation peak shape, relationship with other candidate peaks, andrelationship with other GPS signals detected.

[0053]FIG. 2 shows an example of a data processing system which may beused as a server in various embodiments of the present invention. Forexample, as described in U.S. Pat. No. 5,841,396, the server (201) mayprovide assistance data such as Doppler or other satellite assistancedata to the GPS receiver in a mobile station. In addition, oralternatively, the location server may perform the final positioncalculation rather than the mobile station (after receiving pseudorangesor other data from which pseudoranges can be determined from the mobilestation) and then may forward this position determination result to thebase station or to some other system. The data processing system as alocation server typically includes communication devices 212, such asmodems or network interface. The location server may be coupled to anumber of different networks through communication devices 212 (e.g.,modems or other network interfaces). Such networks include the cellularswitching center or multiple cellular switching centers 225, the landbased phone system switches 223, cellular base stations (not shown inFIG. 2), other GPS signal receivers 227, or other processors or locationservers 221.

[0054] Multiple cellular base stations are typically arranged to cover ageographical area with radio coverage, and these different base stationsare coupled to at least one mobile switching center, as is well known inthe prior art (e.g., see FIG. 1). Thus, multiple base stations would begeographically distributed but coupled together by a mobile switchingcenter. The network 220 may be connected to a network of reference GPSreceivers which provide differential GPS information and may alsoprovide GPS ephemeris data for use in calculating the position of mobilesystems. The network is coupled through the modem or other communicationinterface to the processor 203. The network 220 may be connected toother computers or network components. Also network 220 may be connectedto computer systems operated by emergency operators, such as the PublicSafety Answering Points which respond to 911 telephone calls. Variousexamples of methods for using a location server have been described innumerous U.S. patents, including: U.S. Pat. Nos. 5,841,396, 5,874,914,5,812,087 and 6,215,442.

[0055] The location server 201, which is a form of a data processingsystem, includes a bus 202 which is coupled to a microprocessor 203 anda ROM 207 and volatile RAM 205 and a non-volatile memory 206. Theprocessor 203 is coupled to cache memory 204 as shown in the example ofFIG. 2. The bus 202 interconnects these various components together.While FIG. 2 shows that the non-volatile memory is a local devicecoupled directly to the rest of the components in the data processingsystem, it will be appreciated that the present invention may utilize anon-volatile memory which is remote from the system, such as a networkstorage device which is coupled to the data processing system through anetwork interface such as a modem or Ethernet interface. The bus 202 mayinclude one or more buses connected to each other through variousbridges, controllers and/or adapters as is well known in the art. Inmany situations the location server may perform its operationsautomatically without human assistance. In some designs where humaninteraction is required, the I/O controller 209 may communicate withdisplays, keyboards, and other I/O devices.

[0056] Note that while FIG. 2 illustrates various components of a dataprocessing system, it is not intended to represent any particulararchitecture or manner of interconnecting the components as such detailsare not germane to the present invention. It will also be appreciatedthat network computers and other data processing systems which havefewer components or perhaps more components may also be used with thepresent invention and may act as a location server or a PDE.

[0057] In some embodiments, the methods of the present invention may beperformed on computer systems which are simultaneously used for otherfunctions, such as cellular switching, messaging services, etc. In thesecases, some or all of the hardware of FIG. 2 would be shared for severalfunctions.

[0058] It will be apparent from this description that aspects of thepresent invention may be embodied, at least in part, in software. Thatis, the techniques may be carried out in a computer system or other dataprocessing system in response to its processor executing sequences ofinstructions contained in memory, such as ROM 207, volatile RAM 205,non-volatile memory 206, cache 204 or a remote storage device. Invarious embodiments, hardwired circuitry may be used in combination withsoftware instructions to implement the present invention. Thus, thetechniques are not limited to any specific combination of hardwarecircuitry and software nor to any particular source for the instructionsexecuted by the data processing system. In addition, throughout thisdescription, various functions and operations are described as beingperformed by or caused by software code to simplify description.However, those skilled in the art will recognize what is meant by suchexpressions is that the functions result from execution of the code by aprocessor, such as the processor 203.

[0059] A machine readable medium can be used to store software and datawhich when executed by a data processing system causes the system toperform various methods of the present invention. This executablesoftware and data may be stored in various places including for exampleROM 207, volatile RAM 205, non-volatile memory 206 and/or cache 204 asshown in FIG. 2. Portions of this software and/or data may be stored inany one of these storage devices.

[0060] Thus, a machine readable medium includes any mechanism thatprovides (i.e., stores and/or transmits) information in a formaccessible by a machine (e.g., a computer, network device, personaldigital assistant, manufacturing tool, any device with a set of one ormore processors, etc.). For example, a machine readable medium includesrecordable/non-recordable media (e.g., read only memory (ROM); randomaccess memory (RAM); magnetic disk storage media; optical storage media;flash memory devices; etc.), as well as electrical, optical, acousticalor other forms of propagated signals (e.g., carrier waves, infraredsignals, digital signals, etc.); etc.

[0061]FIG. 3 shows a block diagram representation of a mobile stationaccording to one embodiment of the present invention. The mobile stationcomprises a portable receiver, which combines a communicationtransceiver with GPS receiver for use in one embodiment of the presentinvention. The combined mobile unit 310 includes circuitry forperforming the functions required for processing GPS signals as well asthe functions required for processing communication signals receivedthrough a communication link. The communication link, such ascommunication link 350, is typically a radio frequency communicationlink to another component, such as base station 352 having communicationantenna 351.

[0062] Portable receiver 310 is a combined GPS receiver and acommunication receiver and transmitter. Receiver 310 contains a GPSreceiver stage including acquisition and tracking circuit 321 andcommunication transceiver section 305. Acquisition and tracking circuit321 is coupled to GPS antenna 301, and communication transceiver 305 iscoupled to communication antenna 311. GPS signals (e.g., signal 370transmitted from satellite 303) are received through GPS antenna 301 andinput to acquisition and tracking circuit 321 which acquires the PN(Pseudorandom Noise) codes for the various received satellites. The dataproduced by circuit 321 (e.g., correlation indicators) are processed byprocessor 333 for transmittal by transceiver 305. Communicationtransceiver 305 contains a transmit/receive switch 331 which routescommunication signals (typically RF) to and from communication antenna311 and transceiver 305. In some systems, a band splitting filter, or“duplexer,” is used instead of the T/R switch. Received communicationsignals are input to communication receiver 332 and passed to processor333 for processing. Communication signals to be transmitted fromprocessor 333 are propagated to modulator 334 and frequency converter335. Power amplifier 336 increases the gain of the signal to anappropriate level for transmission to base station 352.

[0063] In one embodiment of the present invention, the combined receiverdetermines one or more signal quality indicators (e.g., magnitude of thecorrelation peak, correlation peak width, signal strength, signal tonoise ratio, signal to interference ratio, relationship with othercandidate peaks, and relationship with other GPS signals detected) forthe determination of the a measurement false alarm probability indicatorfor a measurement (e.g., a pseudorange) obtained at the receiver. In oneembodiment, the combined receiver transmits the signal qualityindicators to the base station for the determination of the measurementfalse alarm probability for the measurement. In one embodiment,processor 333 determines the false alarm probability according to aformula based on the indicators and transmits the probability with themeasurement to the base station through the communication link 351. Inone embodiment, the GPS acquisition and tracking circuit 321 has anAutomatic Gain Control (AGC) system that adjusts the gain lineup, whichmay be analog or digital, such that there is a known total power at theoutput of the analog to digital converter. From the gain of the signalat the input, the distribution of the signal (e.g., Gaussian) and thesignal processing (e.g., by processor 333), the correlation threshold isrelated to the false alarm probability (e.g., through collectingstatistical data or through numerical simulation or theoreticallyanalysis). Numerical simulations or theoretically analyses typicallydepend on the signal processing methods used. For example, in oneembodiment, spurious signals when processing a weak received satellitesignal due to interference by a stronger received signal are reduced byestimating certain characteristics of the stronger signal, creating aninterference waveform based on these estimated characteristics, andsubtracting this interference waveform from a set of correlation outputsfor the weaker signal to remove the interference effects of the strongersignal. More details about the mobile station for reducing interferencein a mobile station can be found in U.S. Pat. Nos. 6,236,354. Whenadditional signal processing operations are used to reduce false alarms(or for other purpose), additional simulation operations or analyses areperformed to correlate the signal quality indicators and the false alarmindicators.

[0064] In one embodiment of the present invention, communicationtransceiver section 305 is capable to use communication signals (e.g.,in the communication link 350) to extract timing indicators (e.g.,timing frames or system time) or to calibrate the local oscillator (notshown in FIG. 3) of the mobile station. More details about the mobilestation for extracting timing indicators or calibrating the localoscillator can be found in U.S. Pat. Nos. 5,874,914 and 5,945,944.

[0065] In one embodiment of the combined GPS/communication system ofreceiver 310, data generated by acquisition and tracking circuit 321 istransmitted over communication link 350 to base station 352. Basestation 352 then determines the location of receiver 310 based on thedata from the remote receiver, the time at which the data were measured,and ephemeris data received from its own GPS receiver or other sourcesof such data. The location data can then be transmitted back to GPSreceiver 310 or to other remote locations. More details about portablereceivers utilizing a communication link are disclosed in commonlyassigned U.S. Pat. No. 5,874,914.

[0066] In one embodiment of the present invention, the combined GPSreceiver includes (or is coupled to) a data processing system (e.g., apersonal data assistant, or a portable computer). The data processingsystem includes a bus which is coupled to a microprocessor and a memory(e.g., ROM, volatile RAM, non-volatile memory). The bus interconnectsvarious components together and also interconnects these components to adisplay controller and display device and to peripheral devices such asinput/output (I/O) devices, which are well known in the art. The bus mayinclude one or more buses connected to each other through variousbridges, controllers and/or adapters as is well known in the art. In oneembodiment, the data processing system includes communication ports(e.g., a USB (Universal Serial Bus) port, a port for IEEE-1394 busconnection). In one embodiment of the present invention, the mobilestation transmits the measurements and the a priori false alarmprobabilities for the measurements (or signal quality indicators) to thedata processing system (e.g., through an I/O port) so that the dataprocessing system can determine the position of the receiver and thereliability of the position solution.

[0067] Although the methods and apparatus of the present invention havebeen described with reference to GPS satellites, it will be appreciatedthat the description are equally applicable to positioning systems whichutilize pseudolites or a combination of satellites and pseudolites.Pseudolites are ground based transmitters which broadcast a PN code(similar to a GPS signal), typically modulated on an L-band carriersignal, generally synchronized with GPS time. Each transmitter may beassigned a unique PN code so as to permit identification by a remotereceiver. Pseudolites are useful in situations where GPS signals from anorbiting satellite might be unavailable, such as tunnels, mines,buildings or other enclosed areas. The term “satellite”, as used herein,is intended to include pseudolites or equivalents of pseudolites, andthe term GPS signals, as used herein, is intended to include GPS-likesignals from pseudolites or equivalents of pseudolites.

[0068] In the preceding discussion the invention has been described withreference to application upon the United States Global PositioningSatellite (GPS) system. It should be evident, however, that thesemethods are equally applicable to similar satellite positioning systems,and in particular, the Russian GLONASS system and the proposed EuropeanGalileo System. The GLONASS system primarily differs from GPS system inthat the emissions from different satellites are differentiated from oneanother by utilizing slightly different carrier frequencies, rather thanutilizing different pseudorandom codes. In this situation substantiallyall the circuitry and algorithms described previously are applicable.The term “GPS” used herein includes such alternative satellitepositioning systems, including the Russian GLONASS system.

[0069] Although the operations in the above examples are illustrated inspecific sequences, from this description, it will be appreciated thatvarious different operation sequences and variations can be used withouthaving to be limited to the above illustrated examples.

[0070] The above examples are illustrated without presenting some of thedetails known in the art; these details can be found in thepublications, such as U.S. Pat. Nos. 5,812,087, 5,841,396, 5,874,914,5,945,944, 5,999,124, 6,061,018, 6,208,290, and 6,215,442, 6,236,354,all of which are hereby incorporated here by reference, as pointed outin the above discussion.

[0071] In the foregoing specification, the invention has been describedwith reference to specific exemplary embodiments thereof. It will beevident that various modifications may be made thereto without departingfrom the broader spirit and scope of the invention as set forth in thefollowing claims. The specification and drawings are, accordingly, to beregarded in an illustrative sense rather than a restrictive sense.

What is claimed is:
 1. A method of position determination for a mobilestation, the method comprising: determining a first measurement forposition determination for the mobile station from positiondetermination signals received at the mobile station; and determining afirst reliability indicator from the signals for the first measurement,the first reliability indicator representing a level of measurementfalse alarm probability for the first measurement.
 2. The method ofclaim 1, further comprising: determining a reliability level from thefirst reliability indicator to represent a probability that a positionfor the mobile station calculated using the measurement is not false. 3.The method of claim 2, wherein the position is calculated at the mobilestation.
 4. The method of claim 1, further comprising: transmitting thefirst measurement and the first reliability indicator to a remote serverfor position determination of the mobile station.
 5. The method of claim1, further comprising: transmitting one or more signal qualityindicators from the mobile station to a remote server, the one or moresignal quality indicators being determined from the signals for thefirst measurement; wherein the first reliability indicator is determinedat the remote server using the one or more signal quality indicators. 6.The method of claim 1, further comprising: determining a secondmeasurement from position determination signals received at the mobilestation; and determining a second reliability indicator from positiondetermination signals for the second measurement, the second reliabilityindicator representing a level of measurement false alarm probabilityfor the second measurement.
 7. The method of claim 6, furthercomprising: calculating a position solution for the mobile station usingthe first and second measurements; and combining the first and secondreliability indicators to determine a reliability of the positionsolution.
 8. The method of claim 6, further comprising: eliminating oneof the first and second measurements from position determination usingthe first and second reliability indicators.
 9. The method of claim 1,wherein the first reliability indicator is determined from at least oneof: a) magnitude of a correlation peak; b) correlation peak width; c)signal strength; d) signal to noise ratio; e) signal to interferenceratio; f) relationship of a correlation peak used for determination ofthe first measurement with one or more candidate peaks; and g)relationship of signals for determination of the first measurement withdetected signals.
 10. The method of claim 1, wherein the firstmeasurement comprises one of: a) a time of arrival of a signal; and b) apseudorange.
 11. A method of position determination for a mobilestation, the method comprising: combining a plurality of measurementfalse alarm indicators to determine a reliability of a positioncalculated using a plurality of measurements, the plurality ofmeasurement false alarm indicators representing levels of a priori falsealarm probability for the plurality of measurements respectively. 12.The method of claim 11, further comprising: calculating the position forthe mobile station using the plurality of measurements.
 13. The methodof claim 11, wherein each of the plurality of measurement false alarmindicators is a value of more than two levels.
 14. The method of claim13, wherein each of the plurality of measurement false alarm indicatorsis a number within a range.
 15. The method of claim 11, furthercomprising: determining one of the plurality of measurement false alarmindicators from one or more signal quality indicators; wherein the oneor more signal quality indicators comprises one of: a) magnitude of acorrelation peak; b) correlation peak shape indicator; c) signalstrength; d) signal to noise ratio; and e) signal to interference ratio.16. A method of position determination for a mobile station, the methodcomprising: eliminating one of a plurality of measurements from positiondetermination using a plurality of a priori false alarm indicators inresponse to a determination that the plurality of measurements are notconsistent, the plurality of a priori false alarm indicators beingdetermined respectively for the plurality of measurements individually.17. The method of claim 16, wherein the one of the plurality ofmeasurements is determined from comparing the plurality of a priorifalse alarm indicators.
 18. The method of claim 16, further comprising:determining a plurality of inconsistency indicators for the plurality ofmeasurements respectively from the plurality of measurements; whereinthe one of the plurality of measurements is determined from weightingthe plurality of inconsistency indicators according to the plurality ofa priori false alarm indicators respectively.
 19. The method of claim16, further comprising: determining whether or not an inconsistencylevel among the plurality of measurements is above a threshold.
 20. Themethod of claim 16, wherein the plurality of a priori false alarmindicators are determined from signals used for determination of theplurality of measurements respectively.
 21. A machine readable mediumcontaining executable computer program instructions which when executedby a data processing system cause the system to perform a method ofposition determination for a mobile station, the method comprising:determining a first measurement for position determination for themobile station from position determination signals received at themobile station; and determining a first reliability indicator from thesignals for the first measurement, the first reliability indicatorrepresenting a level of measurement false alarm probability for thefirst measurement.
 22. The medium of claim 21, wherein the methodfurther comprises: determining a reliability level from the firstreliability indicator to represent a probability that a position for themobile station calculated using the measurement is not false.
 23. Themedium of claim 22, wherein the position is calculated at the mobilestation.
 24. The medium of claim 21, wherein the method furthercomprises: transmitting the first measurement and the first reliabilityindicator to a remote server for position determination of the mobilestation.
 25. The medium of claim 21, wherein the method furthercomprises: transmitting one or more signal quality indicators from themobile station to a remote server, the one or more signal qualityindicators being determined from the signals for the first measurement;wherein the first reliability indicator is determined at the remoteserver using the one or more signal quality indicators.
 26. The mediumof claim 21, wherein the method further comprises: determining a secondmeasurement from position determination signals received at the mobilestation; and determining a second reliability indicator from positiondetermination signals for the second measurement, the second reliabilityindicator representing a level of measurement false alarm probabilityfor the second measurement.
 27. The medium of claim 26, wherein themethod further comprises: calculating a position solution for the mobilestation using the first and second measurements; and combining the firstand second reliability indicators to determine a reliability of theposition solution.
 28. The medium of claim 26, wherein the methodfurther comprises: eliminating one of the first and second measurementsfrom position determination using the first and second reliabilityindicators.
 29. The medium of claim 21, wherein the first reliabilityindicator is determined from at least one of: a) magnitude of acorrelation peak; b) correlation peak width; c) signal strength; d)signal to noise ratio; e) signal to interference ratio; f) relationshipof a correlation peak used for determination of the first measurementwith one or more candidate peaks; and g) relationship of signals fordetermination of the first measurement with detected signals.
 30. Themedium of claim 21, wherein the first measurement comprises one of: a) atime of arrival of a signal; and b) a pseudorange.
 31. A machinereadable medium containing executable computer program instructionswhich when executed by a data processing system cause the system toperform a method of position determination for a mobile station, themethod comprising: combining a plurality of measurement false alarmindicators to determine a reliability of a position calculated using aplurality of measurements, the plurality of measurement false alarmindicators representing levels of a priori false alarm probability forthe plurality of measurements respectively.
 32. The medium of claim 31,wherein the method further comprises: calculating the position for themobile station using the plurality of measurements.
 33. The medium ofclaim 31, wherein each of the plurality of measurement false alarmindicators is a value of more than two levels.
 34. The medium of claim33, wherein each of the plurality of measurement false alarm indicatorsis a number within a range.
 35. The medium of claim 31, wherein themethod further comprises: determining one of the plurality ofmeasurement false alarm indicators from one or more signal qualityindicators; wherein the one or more signal quality indicators comprisesone of: a) magnitude of a correlation peak; b) correlation peak shapeindicator; c) signal strength; d) signal to noise ratio; and e) signalto interference ratio.
 36. A machine readable medium containingexecutable computer program instructions which when executed by a dataprocessing system cause the system to perform a method of positiondetermination for a mobile station, the method comprising: eliminatingone of a plurality of measurements from position determination using aplurality of a priori false alarm indicators in response to adetermination that the plurality of measurements are not consistent, theplurality of a priori false alarm indicators being determinedrespectively for the plurality of measurements individually.
 37. Themedium of claim 36, wherein the one of the plurality of measurements isdetermined from comparing the plurality of a priori false alarmindicators.
 38. The medium of claim 36, wherein the method furthercomprises: determining a plurality of inconsistency indicators for theplurality of measurements respectively from the plurality ofmeasurements; wherein the one of the plurality of measurements isdetermined from weighting the plurality of inconsistency indicatorsaccording to the plurality of a priori false alarm indicatorsrespectively.
 39. The medium of claim 36, wherein the method furthercomprises: determining whether or not an inconsistency level among theplurality of measurements is above a threshold.
 40. The medium of claim36, wherein the plurality of a priori false alarm indicators aredetermined from signals used for determination of the plurality ofmeasurements respectively.
 41. A data processing system for positiondetermination for a mobile station, the data processing systemcomprising: means for determining a first measurement for positiondetermination for the mobile station from position determination signalsreceived at the mobile station; and means for determining a firstreliability indicator from the signals for the first measurement, thefirst reliability indicator representing a level of measurement falsealarm probability for the first measurement.
 42. The data processingsystem of claim 41, further comprising: means for determining areliability level from the first reliability indicator to represent aprobability that a position for the mobile station calculated using themeasurement is not false.
 43. The data processing system of claim 42,wherein the position is calculated at the mobile station.
 44. The dataprocessing system of claim 41, further comprising: means fortransmitting the first measurement and the first reliability indicatorto a remote server for position determination of the mobile station. 45.The data processing system of claim 41, further comprising: means fortransmitting one or more signal quality indicators from the mobilestation to a remote server, the one or more signal quality indicatorsbeing determined from the signals for the first measurement; wherein thefirst reliability indicator is determined at the remote server using theone or more signal quality indicators.
 46. The data processing system ofclaim 41, further comprising: means for determining a second measurementfrom position determination signals received at the mobile station; andmeans for determining a second reliability indicator from positiondetermination signals for the second measurement, the second reliabilityindicator representing a level of measurement false alarm probabilityfor the second measurement.
 47. The data processing system of claim 46,further comprising: means for calculating a position solution for themobile station using the first and second measurements; and means forcombining the first and second reliability indicators to determine areliability of the position solution.
 48. The data processing system ofclaim 46, further comprising: means for eliminating one of the first andsecond measurements from position determination using the first andsecond reliability indicators.
 49. The data processing system of claim41, wherein the first reliability indicator is determined from at leastone of: a) magnitude of a correlation peak; b) correlation peak width;c) signal strength; d) signal to noise ratio; e) signal to interferenceratio; f) relationship of a correlation peak used for determination ofthe first measurement with one or more candidate peaks; and g)relationship of signals for determination of the first measurement withdetected signals.
 50. The data processing system of claim 41, whereinthe first measurement comprises one of: a) a time of arrival of asignal; and b) a pseudorange.
 51. A data processing system for positiondetermination for a mobile station, the data processing systemcomprising: means for combining a plurality of measurement false alarmindicators to determine a reliability of a position calculated using aplurality of measurements, the plurality of measurement false alarmindicators representing levels of a priori false alarm probability forthe plurality of measurements respectively.
 52. The data processingsystem of claim 51, further comprising: means for calculating theposition for the mobile station using the plurality of measurements. 53.The data processing system of claim 51, wherein each of the plurality ofmeasurement false alarm indicators is a value of more than two levels.54. The data processing system of claim 53, wherein each of theplurality of measurement false alarm indicators is a number within arange.
 55. The data processing system of claim 51, further comprising:means for determining one of the plurality of measurement false alarmindicators from one or more signal quality indicators; wherein the oneor more signal quality indicators comprises one of: a) magnitude of acorrelation peak; b) correlation peak shape indicator; c) signalstrength; d) signal to noise ratio; and e) signal to interference ratio.56. A data processing system for position determination for a mobilestation, the data processing system comprising: means for eliminatingone of a plurality of measurements from position determination using aplurality of a priori false alarm indicators in response to adetermination that the plurality of measurements are not consistent, theplurality of a priori false alarm indicators being determinedrespectively for the plurality of measurements individually.
 57. Thedata processing system of claim 56, wherein the one of the plurality ofmeasurements is determined from comparing the plurality of a priorifalse alarm indicators.
 58. The data processing system of claim 56,further comprising: means for determining a plurality of inconsistencyindicators for the plurality of measurements respectively from theplurality of measurements; wherein the one of the plurality ofmeasurements is determined from weighting the plurality of inconsistencyindicators according to the plurality of a priori false alarm indicatorsrespectively.
 59. The data processing system of claim 56, furthercomprising: means for determining whether or not an inconsistency levelamong the plurality of measurements is above a threshold.
 60. The dataprocessing system of claim 56, wherein the plurality of a priori falsealarm indicators are determined from signals used for determination ofthe plurality of measurements respectively.
 61. A mobile station of aposition determination system, the mobile station comprising: a signalreceiving circuit to receive position determination signals; a processorcoupled to the signal receiving circuit, the process determining a firstmeasurement for position determination for the mobile station from thesignals, the processor determining a first reliability indicator fromthe signals for the first measurement, the first reliability indicatorrepresenting a level of measurement false alarm probability for thefirst measurement.
 62. The mobile station of claim 61, wherein theprocessor further determines a reliability level from the firstreliability indicator to represent a probability that a position for themobile station calculated using the measurement is not false.
 63. Themobile station of claim 61, further comprising: a communication sectioncoupled to the processor, the communication section transmitting thefirst measurement and the first reliability indicator to a remote serverfor position determination of the mobile station.
 64. The mobile stationof claim 61, wherein the processor further determines a secondmeasurement and a second reliability indicator for the secondmeasurement from position determination signals received by the signalreceiving circuit; wherein the second reliability indicator represents alevel of measurement false alarm probability for the second measurement.65. The mobile station of claim 64, wherein the processor furthercalculates a position solution for the mobile station using the firstand second measurements and combines the first and second reliabilityindicators to determine a reliability of the position solution.
 66. Themobile station of claim 64, wherein the processor further eliminates oneof the first and second measurements from position determination usingthe first and second reliability indicators.
 67. The mobile station ofclaim 61, wherein the first reliability indicator is determined from atleast one of: a) magnitude of a correlation peak; b) correlation peakwidth; c) signal strength; d) signal to noise ratio; e) signal tointerference ratio; f) relationship of a correlation peak used fordetermination of the first measurement with one or more candidate peaks;and g) relationship of signals for determination of the firstmeasurement with detected signals.
 68. The mobile station of claim 61,wherein the first measurement comprises one of: a) a time of arrival ofa signal; and b) a pseudorange.
 69. A data processing system forposition determination for a mobile station, the data processing systemcomprising: a memory to store a plurality of measurement false alarmindicators and a plurality of measurements, the plurality of measurementfalse alarm indicators representing levels of a priori false alarmprobability for the plurality of measurements respectively; and aprocessor coupled to the memory, the processor combining the pluralityof measurement false alarm indicators to determine a reliability of aposition calculated using the plurality of measurements.
 70. The dataprocessing system of claim 69, wherein the processor further calculatesthe position for the mobile station using the plurality of measurements.71. The data processing system of claim 69, wherein each of theplurality of measurement false alarm indicators is a value of more thantwo levels.
 72. The data processing system of claim 71, wherein each ofthe plurality of measurement false alarm indicators is a number within arange.
 73. The data processing system of claim 69, wherein the processorfurther determines one of the plurality of measurement false alarmindicators from one or more signal quality indicators; wherein the oneor more signal quality indicators comprises one of: a) magnitude of acorrelation peak; b) correlation peak shape indicator; c) signalstrength; d) signal to noise ratio; and e) signal to interference ratio.74. A data processing system for position determination for a mobilestation, the data processing system comprising: a memory to store aplurality of measurements and a plurality of a priori false alarmindicators, the plurality of a priori false alarm indicators beingdetermined respectively for the plurality of measurements individually aprocessor coupled to the memory, the processor eliminating one of theplurality of measurements from position determination using theplurality of a priori false alarm indicators in response to adetermination that the plurality of measurements are not consistent. 75.The data processing system of claim 74, wherein the one of the pluralityof measurements is determined from comparing the plurality of a priorifalse alarm indicators.
 76. The data processing system of claim 74,wherein the processor further determines a plurality of inconsistencyindicators for the plurality of measurements respectively from theplurality of measurements; wherein the one of the plurality ofmeasurements is determined from weighting the plurality of inconsistencyindicators according to the plurality of a priori false alarm indicatorsrespectively.
 77. The data processing system of claim 74, wherein theprocessor further determines whether or not an inconsistency level amongthe plurality of measurements is above a threshold.
 78. The dataprocessing system of claim 74, wherein the plurality of a priori falsealarm indicators are determined from signals used for determination ofthe plurality of measurements respectively.